It seems to me that the comparison is a little unbalanced. Sonore and SOtM are very similar in terms of functionality but Lumin U1 mini is a machine with many more features ... it would seem to me to compare apples and oranges.
I have SOtM SMS 200 Neo (not Ultra) and I find that it works very well despite not having linear power, the improvement of SQ compared to Mac + Audirvana has been remarkable for me.
Regarding the Sonore and SoTM features, they have very similar sw, it has the same origin even if SoTM then followed its own path, they offer MPD UPNP/DLNA roon Ready HQPlayer NAA LMS/Squeezelite Shairport Bubbleupnpserver and just the SOtM Librespot and Minimserver.
I think the comparison should be made on the availability of streaming services such as Qobuz, Tidal (MQA) etc ...
I am not very interested in Tidal and Qobuz but I have tried Tidal these days and, as far as I have been able to understand, the service is accessible only for cd quality, MQA is not available. Furthermore, the availability of navigation options is rather poor compared to the original Tidal app.
I can imagine that Sonore is also on the same level, but I could be wrong.
Very different is the Lumin U1 mini that I do not own but of which I have carefully read the specifications.
I use use the Lumin app which I find exceptional.
Lumin allows you to upscale to DSD, access the most popular streaming services and Web Radios and on paper it is perfectly compatible with Tidal MQA. Last but not least the fact that users talk about it very well also in terms of SQ.
The support offered directly by Lumin on this forum is also effective, precise and almost immediate (considering the time difference).
That said my vote is for Lumin U1 mini